Wireless telecommunication systems are well known in the art. In order to provide global connectivity for wireless systems, standards have been developed and are being implemented. One current standard in widespread use is known as Global System for Mobile Telecommunications (GSM). This is considered as a so-called Second Generation mobile radio system standard (2G) and was followed by its revision (2.5G). GPRS and EDGE are examples of 2.5G technologies that offer relatively high speed data service on top of (2G) GSM networks. Each one of these standards sought to improve upon the prior standard with additional features and enhancements. In January 1998, the European Telecommunications Standard Institute—Special Mobile Group (ETSI SMG) agreed on a radio access scheme for Third Generation Radio Systems called Universal Mobile Telecommunications Systems (UMTS). To further implement the UMTS standard, the Third Generation Partnership Project (3GPP) was formed in December 1998. 3GPP continues to work on a common third generational mobile radio standard.
A typical UMTS system architecture in accordance with current 3GPP specifications is depicted in FIG. 1. The UMTS network architecture includes a Core Network (CN) interconnected with a UMTS Terrestrial Radio Access Network (UTRAN) via an interface known as Iu which is defined in detail in the current publicly available 3GPP specification documents. The UTRAN is configured to provide wireless telecommunication services to users through wireless transmit receive units (WTRUs), known as User Equipments (UEs) in 3GPP, via a radio interface known as Uu. The UTRAN has one or more Radio Network Controllers (RNCs) and base stations, known as Node Bs in 3GPP, which collectively provide for the geographic coverage for wireless communications with UEs. One or more Node Bs is connected to each RNC via an interface known as Iub in 3GPP. The UTRAN may have several groups of Node Bs connected to different RNCs; two are shown in the example depicted in FIG. 1. Where more than one RNC is provided in a UTRAN, inter-RNC communication is performed via an Iur interface.
Communications external to the network components are performed by the Node Bs on a user level via the Uu interface and the CN on a network level via various CN connections to external systems.
In general, the primary function of base stations, such as Node Bs, is to provide a radio connection between the base stations' network and the WTRUs. Typically a base station emits common channel signals allowing non-connected WTRUs to become synchronized with the base station's timing. In 3GPP, a Node B performs the physical radio connection with the UEs. The Node B receives signals over the Iub interface from the RNC that control the radio signals transmitted by the Node B over the Uu interface.
A CN is responsible for routing information to its correct destination. For example, the CN may route voice traffic from a UE that is received by the UMTS via one of the Node Bs to a public switched telephone network (PSTN) or packet data destined for the Internet. In 3GPP, the CN has six major components: 1) a serving General Packet Radio Service (GPRS) support node; 2) a gateway GPRS support node; 3) a border gateway; 4) a visitor location register; 5) a mobile services switching center; and 6) a gateway mobile services switching center. The serving GPRS support node provides access to packet switched domains, such as the Internet. The gateway GPRS support node is a gateway node for connections to other networks. All data traffic going to other operator's networks or the internet goes through the gateway GPRS support node. The border gateway acts as a firewall to prevent attacks by intruders outside the network on subscribers within the network realm. The visitor location register is a current serving networks ‘copy’ of subscriber data needed to provide services. This information initially comes from a database which administers mobile subscribers. The mobile services switching center is in charge of ‘circuit switched’ connections from UMTS terminals to the network. The gateway mobile services switching center implements routing functions required based on current location of subscribers. The gateway mobile services also receives and administers connection requests from subscribers from external networks.
The RNCs generally control internal functions of the UTRAN. The RNCs also provides intermediary services for communications having a local component via a Uu interface connection with a Node B and an external service component via a connection between the CN and an external system, for example overseas calls made from a cell phone in a domestic UMTS.
Typically a RNC oversees multiple base stations, manages radio resources within the geographic area of wireless radio service coverage serviced by the Node Bs and controls the physical radio resources for the Uu interface. In 3GPP, the Iu interface of an RNC provides two connections to the CN: one to a packet switched domain and the other to a circuit switched domain. Other important functions of the RNCs include confidentiality and integrity protection.
In code division multiple access (CDMA) communication systems, multiple communications are sent in a shared spectrum. These communications are distinguished by their channelization codes. To more efficiently use the shared spectrum, hybrid time division multiple access (TDMA)/CDMA communication systems time divide the shared bandwidth into repeating frames having a specified number of timeslots. A communication is sent in such a system using one or multiple timeslots and one or multiple codes. For example, a UMTS time division duplex (TDD) communication system using CDMA uses fifteen (15) timeslots. In TDD, a particular cell's timeslot is used only for either uplink or downlink communications. Such conventional communications systems can be configured to utilize Forward Error Correction (FEC) in connection with wireless communications.
Adaptive modulation and coding (AM&C) are used to deal with the variety of bandwidths required for various communications. In AM&C, the modulation and coding scheme for transmitting data is varied to more efficiently use radio resources. To illustrate, the modulation used for data may be varied, such as using binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), or M-ary quadrature amplitude modulation. Furthermore, the data may be assigned a single code in a timeslot, multiple codes in a timeslot, a single code in multiple timeslots or multiple codes in multiple timeslots.
Adaptive modulation enables a communication system to exploit the allocated channel bandwidth. Proper use of adaptive modulation requires some information on the state of the channel. Based on the health of the channel, a system can increase or decrease the modulation order to adapt the data rate to the usable part of the channel. Usually, an estimate of the received signal-to-interference/noise-ratio, received-signal-strength or even noise level of the signal that all could be an indicative of the bit-error-rate, are used as an indication of the health of the channel.
A conventional receiver configuration is illustrated in FIG. 2. A Front-end Receiver receives the modulated signals and strips a received signal's carrier frequency to provide a modulated communication signal for receiver processing. The modulated signal is processed by a demodulator of the receiver which typically includes a receive processor configured to output a demodulated version of the signal and a signal quality estimator configured to measure and collect information about the signal and output quality estimates such as a signal to noise ratio (SNR), signal to Interference Ratio (SNIR) or other metrics that are generated over selected time periods. Conventionally, such metrics which are generated over time in conjunction with demodulation are used to determine a signal quality indicator. The signal quality indicator can be generated by a transmit processor for inclusion in a signal as adaptive modulation feedback which is then modulated and sent back to the wireless station that had originally transmitted the received modulated signal. The station originating the modulated transmission can then use the adaptive modulation feedback to adjust the modulation of the signals it is transmitting by, inter alia, deciding how the order of modulation and/or the data-rate is to be adapted.
The inventors' have recognized that using an estimate of the signal-to-noise ratio or similar quality measures will not necessarily produce quality indicators in a manner to most effectively apply an adaptive feedback scheme. The conventional signal quality metrics produced in connection with demodulation may not be accurate and may not be easily mapped to a certain bit-error-rate or a quality-of-service requirement. This is especially more pronounced when a powerful channel-coding scheme is used. Also, since those types of measurements require accumulation of several demodulated symbols, the estimation becomes available with some delay. In some cases, the delay is not acceptable since the error-rate had already been significantly peaked and the performance of the link been deteriorated. Accordingly, the inventors' have recognize a need for an alternative scheme for providing adaptive modulation feedback.